In recent years there has been increased interest throughout the world in the use of proton radiation therapy for treatment of cancer and independent studies project a 20% annual increase in the installed base. The replacement of X-ray therapy with proton therapy will have substantial long term benefit to patients due to greatly reduced long and short term toxicity side effects. Such effects also have substantial costs associated with their treatment that may continue for many years after treatment. Making the cost of delivering proton therapy cost competitive to that of X-ray therapy not only makes a superior treatment mode available, but will also result in substantial long term savings to health care providers. The capital and operating cost of extant systems is a major limiting factor. The procedure referred to as Spot Beam Scanning (SBS), where scanning of a small beam 3D spot (voxel) takes advantage of the physical properties of protons and provides the ultimate in tumor conformality is now rapidly being introduced for use in for dose delivery. SBS eliminates the need for patient-specific devices (collimators and compensators) that are both expensive to manufacture and add considerably to the time needed to deliver each dose to the patient, thereby further reducing operating costs. The SBS approach however is more sensitive to organ motion than traditional procedures. To overcome this fast SBS of the target volume to greatly reduce dose delivery times into the millisecond (ms) time scale is optimal. Phenix believes that fast scanning not only makes the SBS more suitable for treating moving targets but also enables faster dose delivery as needed for new prospective treatment protocols using protons, such as lung tumors. The increasing use of accelerators by vendors that deliver beam in short ms pulses places further challenges on detectors than can rapidly verify the area treated and the magnitude of the dose delivered to the tumor. These dual challenges require detectors that can monitor both the position and dose delivered in real-time and provide rapid feedback to the accelerator to modify further dose to be delivered as required. None of the extant systems now available can satisfy these demands. The Specific Aims in this grant application are to perform the research needed to further develop the use of a novel very fast gas scintillation technique to measure the dose delivered and the spot position on a sub-millisecond time scale based on the prototype developed in Phase I.